Virions of RNA tumor viruses contain 3 or 4 molecules of 35 S genomic RNA plus 70-80 molecules of small RNA (4-7S). This small RNA accounts for approximately 15 percent of the viral RNA. Some of these small RNAs have specific functions during infection and transformation; for example, initiation of viral DNA synthesis occurs by addition of deoxyribonucleotides to the 3' end of one of the small RNAs, the primer for DNA synthesis. Other small RNAs may be host RNAs included in the virion during budding or they may be degradation products of larger molecules. We plan to characterize the uniformly p32-labeled small RNAs of Schmidt-Ruppin-D strain of Rous sarcoma virus (SR-D), using 2- dimensional polyacrylamide gel electrophoresis (2-D gel) and fingerprinting of nuclease digests of the RNAs. Since the 2-D gel separates and purifies most 4-7S molecules, it can be used analytically (to screen various RNA preparations for the presence or absence of particular molecules) and preparatively, for purification before oligonucleotide fingerprint analysis. We plan to characterize the SR-D small RNAs with respect to their relative molar yields, their location within the virion, and their association with the genome RNA. We shall determine the nucleotide sequence of three SR-D small RNAs, one of which is the DNA-primer, in order to relate the structures of these molecules to their functions. We shall also compare the small RNAs of other transforming and non-transforming avian RNA tumor viruses with the SR-D RNAs, to determine how the presence of these molecules in the virion might be related to viral physiology and cell transformation.